very good question... You should set it to 10750. But the way that LNB works is that it works like a normal standard LNB for 11.7 to 12.2 Vertical, but for horizontal it uses a higher LO and stacks the resulting IF on top of the vertical signal
So basically from 950 to 1450 you get the vertical transponders and from 1650 to 2150 you get the horizontal transponders, without switching voltage. so in the receiver, just set it to one polarization and 10750 as the LO. Just expect to see Horizontal transponders show up with unusual frequencies like 12630 MHz etc. The beauty of those is that you could feed them to multiple receivers using spliters.
there's a great explanation here:
Satellite LNB: What is it, how does it work and where do I buy one? (scroll down to the "Stacked Frequency LNBs" section
the other LNB that is labelled "BSS Stacked" works the same way, but with the 11250 LO, for the 12.2-12.7 band